1. Field of the Invention
The present invention relates to a fluid sampling device comprising a thermal control valve.
2. Description of the Prior Art
Two prior art methods are known.
The first approach, is described for example by:
Ungerer P. et al, 1988, in Kinetic Modelling of Oil Cracking, Org. Geochem., 13,857-868, carries out pyrolyses of increasing duration. At the end of each of the successive experiments, the kinetics are stopped by means of an abrupt temperature drop. The conversion coefficients and the reaction rates are thus acquired at different times.
The second approach performs successive samplings during the progress of a single experiment. Considering the duration, of pyrolysis reactions, this approach has the advantage of reducing the total acquisition time. The entire kinetics can be obtained with a single handling whereas the number of experiments should be multiplied with the first technique. The method of operation through sampling also allows a determination that the reactive medium has always had the same (thermal and therefore reaction) history in time, which is not always the case when experiments are repeated. On the other hand, using successive samplings requires a greater reaction volume in order to make sure that the sum of the various aliquots extracted in the course of time will not lead to considerable changes in the operating conditions of the reaction system. The implementation difficulty of this approach at high pressures is due to the considerable dead volume inherent in conventional needle valves.
The fluid sampling device according to the invention, which comprises a sampling cell for collecting fluid, provided with an inlet hole, is characterized in that the sampling cell is insulated by a thermal control valve consisting of a plug made from a solid low-melting temperature material that is made permeable to the fluid by temporary heating.
The device of the invention lends itself to many applications where control of an evolutionary process or characterization of phase equilibria requires successive and distinct fluid samplings while reducing the effects of contamination due to dead volumes remaining in the sampling circuits.
The sampling device according to the invention can be used for example to take fluid samples within the scope of oil or fluid pyrolyses in closed reactors. In order to be representative of the evolution of natural basins, these reactions last for several days or even several weeks. The kinetics of such reactions can be obtained according to two approaches.
According to a preferred embodiment, the plug that seals the inlet hole is made from a stable melting temperature eutectic metal alloy such as Wood""s metal for example.
According to an embodiment, the device of the invention comprises an intermediate cell with a central channel provided with a plug made of the solid material, which communicates with an inlet with a first end and an outlet with the opposite end thereof, and is suited to tightly fit into the inlet hole of the sampling cell, a connection for connecting the sampling cell to the intermediate cell, an element associated with a seal for connecting, at the inlet of the intermediate cell, a fine linking tube to a reactor producing the fluid to be sampled.
According to an embodiment suited for fluid sampling under elevated pressure, the sampling cell is provided with a fine inlet channel, the section and the length of this inlet channel and those of the central channel of the intermediate cell are so selected that the plugs formed by cooling of the material are sealed against the fluid sampled.
The method for implementing the device according to the invention comprises: a sampling cell preparation step comprising transfer of a certain volume of the material in the liquid state into the cell, suction of the fluid contained in the cell, transfer of the volume of material into the inlet of the cell and cooling thereof so as to form a sealed plug; and
a sampling step comprising communicating the sampling cell with a vessel containing the fluid to be sampled, and temporary heating of the plug (which leads to the melting thereof) in order to make it permeable to the fluid.
According to an embodiment, the method further comprises a step of preparation of an intermediate cell in order to form therein a second solid plug made from the material, the sampling also comprising combined heating of the second plug in order to make it permeable to the fluid.
A capillary tube is preferably used to connect the reactor to the intermediate cell so as to minimize dead volumes.
Fluid ampoules are thus available for subsequent treatments. There is no constraint concerning the conservation thereof and this storage method allows high flexibility during later analyses. The consequence of certain sampling methods is the use of suited analysis techniques: in many fluid analysis cases, specific chromatography injectors have to be used. The sampling mode described hereafter requires no adjustment of existing sensing devices and all of the conventional devices can be used.
A valve of this type has many advantages in comparison with conventional valves used in laboratory devices:
The valve is economical while providing perfect sealing. The installation thereof is much simpler than that of a conventional valve. The installation simplicity thereof, combined with its low cost, makes it possible to manufacture sample ampoules that can optionally be expandable. A batch of ampoules containing fluid samples representative of successive times of a reaction spread over a relatively long period can be readily constituted and it is therefore possible to simplify the organization of the step of acquisition and processing of data relative to this reaction, which can last for a shorter time.
The characteristics of this type of valve are well reproducible, which facilitates comparisons between the successive fluid samples. It is also possible with this type of valve to reduce dead volumes to very little so that trails are negligible and the successive samples are entirely independent of one another.
Once the sampling is performed, the sampling cell can be removed, the intermediate cell with its solidified xe2x80x9cthermal valvexe2x80x9d tightly insulates the reaction chamber, and a new fluid recovery cell can be set for a new sampling operation.